Liquid, and especially concentrated liquid, pharmaceutical compositions offer several advantages over solid compositions. Liquids are easy to swallow and provide an excellent vehicle for the uniform delivery of pharmaceutical agents. Moreover, liquids provide a rapid onset of pharmacologic action, since the composition does not first have to disintegrate and dissolve in the gastrointestinal tract. Likewise, concentrated liquid compositions offer certain distinct advantages, such as faster onset of efficacy due to the high concentration of pharmaceutical agents. Consumers prefer a concentrated liquid composition due to the ease of dosing, and less volume of doses.
These advantages notwithstanding, it is, however, often difficult to prepare such compositions using the desired pharmaceutical agents. Many pharmaceutical agents are poorly soluble and, therefore, require relatively large volumes of solvent for dissolution, resulting in impractically large doses. Furthermore, the situation becomes even more complicated when multiple pharmaceutical agents are involved, and particularly where the soluble pharmaceutical agent is in combination with additional water soluble pharmaceutical agent(s) that may hinder the efficacy of at least one or more of the pharmaceutical agents and produce a bitter taste that consumers would be discouraged from using.
Guaifenesin is a well known pharmaceutical agent, classified as an expectorant, and is sold as tablets or syrups under many brand names. Single-ingredient formulations of guaifenesin are available, and it is also included in many other over-the-counter cough and cold remedy combinations, usually in conjunction with dextromethorphan and/or acetominophen and/or ephedrine/pseudoephedrine or phenylephrine. Guaifenesin is a component of Robitussin™ DM, Robitussin™ DM MAX, Robitussin™ CF Max and other well known brand names. Generally the concentration of guaifenesin in most over-the-counter cough medicines is approximately 100 mg/5 mL liquid to 200 mg/5 mL. As an example, the Robitussin™ CF Max product contains 100 mg/5 mL and Mucinex™ Fast-Max™ Severe Congestion and Cough product contains 100 mg guaifenesin/5 mL liquid.
It has been reported in the literature that the aqueous solubility of guaifenesin, a soluble drug in water, could be significantly reduced in the presence of salts, sugars, and higher concentrations of cosolvents. See “Solubility of Guaifenesin In The Presence Of Common Pharmaceutical Additives,” Narasimhan Mani, Pharm Dev Technol 8:385-96. 2003.
Many commercially available over-the-counter liquid cold, cough, flu, fever, and/or allergy preparations contain pseudoephedrine as an active agent. Although such preparations have been useful, misuse of such products as a starting material for synthesis of illicit substances has lead to the desire to find alternatives that are not suitable for such illicit synthesis. Phenylephrine is a potential alternative agent. However, phenylephrine is susceptible to degradation. The degradation is typically facilitated in excipient compositions of the type typically used with pseudoephedrine.
Accordingly, it would be desirable to have a palatable, stable, liquid composition with inhibited precipitation of pharmaceutical agents, such as guaifenesin, alone or in combination with additional pharmaceutical agents, such as phenylephrine, in a mixture of polyethylene glycol, polyvinylpyrrolidone and propylene glycol.